Electromagnetic powder couplings

ABSTRACT

An electromagnetic powder coupling comprising an outer rotor formed by two pole piece halves centered on lateral cheeks of an amagnetic material, an excitation coil is housed between the two pole piece halves which define an air gap around an inner rotor, the centering of the pole piece halves being effected by a convex cylindrical face machined on each of these pole piece halves in the immediate vicinity of the air gap in order to fit on the cylindrical face opposite a peripheral ring provided for this purpose on the corresponding cheek, while, on the other hand, the connection of the two pole piece halves in the middle of the air gap is ensured, without direct contact between them, by an amagnetic axially-slidable coaxial sleeve which is separated from the coil by a free space.

United States Patent [151 Ruget 1 ELECTROMAGNETIC POWDER COUPLINGS ['75]Inventor: Gabriel Ruget, Saint Etienne, Loire,

France a [73] Assignee: Creusot-Loire, Paris, France [22] Filed: Oct;19, 1970 211 App1.No.: 82,055.",

[30] Foreign Application Priority Data Oct. 17, 1969 France 6936127 [52]U.S. Cl. .L 192/215, 335/217 [51] Int. Cl F16d 27/00 [58] Field ofSearch 192/215; 335/217 [56] 1 References Cited UNITED STATES PATENTS2,878,913 3/1959 Jaeschke 192/215 FOREIGN PATENTS OR APPLICATIONS1,046,420 12/1958 Germany 192/215 June 19, 1973 1,115,084 10/1961Germany 192/215 Primary Examiner-Benjamin W. Wyche AssistantExaminerRandall Heald Attorney-Irving M. Weiner [57] ABSTRACT order tofit on the cylindrical face opposite a peripheral ring provided for thispurpose on the corresponding cheek, while, on the other hand, theconnection of the two pole piece halves in the middle of the air gap isensured, without direct contact between them, by an amagneticaxially-slidable coaxial sleeve which is separated from the coil by afree space.

9 Claims, 5 Drawing Figures "mum M 3' 739.687

INVENTOR GABRIEL RUGET BY ATTORNEY Pmmaowm 3.739.897

' sum or 2 INVENTOR GABRIEL P GET 1 ELECTROMAGNETIC POWDER COUPLINGSThis invention relates toan electromagnetic powder coupling havingmeans. for protecting it against the effect of. thermal shocks.

It is. known that an electromagnetic powder coupling comprises an outerrotor and an inner rotor separated by an air gap in which is locatedmetal, for example, steel powder. The outer rotor comprises two polepiece halves between which is housed an electromagnetic coil which issupplied fromoutside byrotatingcontacts. Twolateral checks are attachedto the sides of the pole piece halves in'order to ensure the centeringof theouter rotor on the inner rotor.

It'isknown toplace the two pole piece halves in contact with each otherby means of an annular lip of slight thickness placed around thecentralregion of the air gap, in order to produce, without anysignificant-magnetic leakage, a magnetic shunt capable of closing theresidual field at the time of cutting the excitation currentto the coil,in order to obtain an immediate disconnection of the two rotors. It isknown thatif the speed of heating-up of the coupling, when operating,reaches a certain level, the. metal of the two pole piece halves expandsand exceeds its elastic limit at the level of the two lipsin contactwhich form the magnetic shunt. The metal is compressed in thisregionand, when the coupling cools; the contraction causes a clearance whichresults from the thermal stresses. The magnetic powder tends to packintothis gap, such that during the next heating-up, the phenomenon isincreased andso on. Gradually, the assembly of the outerrotor-becomes-deformed due to buckling, the air gap reduces in thecentre, and the powder tends toaccumulate in the coil housing by passingthroughthe gap between the two pole piece halves of the outerrotor, suchthat there is little left in the airgap. In the course of time, theperformance of the coupling deteriorates, its operating temperatureincreases and this phenomenon can increase until. the coupling isdestroyed.

Another important point in the heating of known electromagnetic powdercouplings is constituted bythe centeringof the outer rotor on thelateral cheeks. Traditionally, this centering isensured by shoulders,machined in the lateral faces of the two pole piece halves and whichabut against the outer'peripheral face of the cheeks. The latter-are:made froman amagnetic material,and they have a coefficient of expansiongreater by almost 60 percent than that of the extra soft steel whichforms the pole piece halves. The mounting of the checks in the polepiece halves. is effected without clearance when cold. Consequently,when the coupling heats up during operation, thelateral. cheeks tend toexpand more than the pole piece halves which fasten them together,suchthat here too there is a risk of causing thermal stresses in [thecase of exaggerated heating.

After coolingand contraction, the pole piece halvesof the outer rotorare nolongercorrectly-centred on the cheeks. This causesunbalancesandgives the air gap an irregular shape which is-harmful to the properoperation of the coupling.

Finally, the performances of an electromagnetic, powder coupling. ofknown typearelimited: by the consequences of heating, one the one hand,at the level of the m'agneticshunt which connects thetwo pole piecehalves of theouter-rotor, and, on the other hand, in the region wherethese pole piece halves are centred on the lateral cheeks.

An object of the present invention is to obviate or mitigate thesedisadvantages and to push back this upper limit due to heating, in orderto improve the performance of the coupling.

An electromagnetic powder coupling according to the invention comprisesan outer rotor formed by two pole piece halves of extra soft steelcentredon the lateral'cheeks of amagnetic material, while an excitationcoil is housed between the two pole piece halves which define an air gaparound an air gap around an inner rotor, and it is characterized inthat, on the one hand, the centering of the pole piece halves iseffected by a convex, cylindrical face machined on each of these polepiece halves in order to fit over the inner cylindrical face of aperipheral ring provided for this purpose on the corresponding cheek,whilst, on the other hand, the connection of the two pole piece halvesin the middle of the air gap is ensured, without direct contact betweenthem, by an amagnetic coaxial sleeve fitted, with the possibility ofaxial sliding in two grooves cut opposite each other in the pole piecehalves. Preferably, this sleeve has in its centre a rib projectinginwardly, and the inner diameter of which is equal to the inner diameterof the two adjacent pole piece halves which define the air gap aroundthe inner rotor. In addition, the lip of each pole piece half which islocated between this sleeve and the air gap of the coupling ispreferably bevelled.

Due to this arrangement, the tendency of the powder to pack between thepole piece halves and the sleeve is avoided, whilst reducing thesignificance of the magnetic shunt formed by the powder between the twopole piece halves.

An embodiment of the present invention will now be described, by way ofexample, with reference to theaccompanying drawings, in which:

FIG. 1, is an axial section of an electromagnetic powder couplingaccording to the invention;

FIG. 2, is a partial end view in the direction of the arrow II in FIG.1;

FIG. 3, is a partial section showing, a detail of FIG. 1;

FIG. 4, illustrates, on a still larger scale, a detail of on a largerscale,

FIG. 3; and

of the pole piece half FIG. 5, shows the operation of the coupling forcentering a check when the coupling operates hot.

There is shown in the drawings, an electromagnetic powder coupling whichcomprises an inner rotor I separated from the outer rotor by an air gap2 where the steel powder is located. The outer rotor is formed by twopole piece halves 3 and 4 of soft steel provided with lateral checks 5and 6 of amagnetic material. Between the two pole piece halves 3 and 4is housed an excitation coil 7 which is supplied externally by means ofrotating contacts 8 and 9.

Each cheek 5.or 6 is provided with a centering ring 10 or 11 whichprojects in the direction of the coupling pole piece half 3m 4. Thefollowing description relates to the ring 11 of the Check 6 and itsmounting on the pole piece half 4, but it is understood that themounting is similar for the ring 10 of the cheek 5 fixed on the polepiece half 3.

The ring 11 has a concave cylindrical face 12 (FIGS) and it is on thisinner cylindrical face that the centering 4 is effected when cold. Forthis a first annular groove 13 is cut on the side of the pole piece half4, so as to define a convex cylindrical face 14 which, when cold, ismounted contiguously without play against the inner face 12 of the ring11. The fixation is ensured by pins or tie-bolts 15 which pass entirelythrough the assembly 10, 3, 4, 11.

Finally, a radial clearance 16 is provided between the outer cylindricalface 17 of the ring ll'and the inner cylindrical face 18 of the groove13.

The coefficient of expansion of the material of the cheeks and 6 isclearly greater than that of the soft steel of the pole piece halves 3and 4, and therefore it will be understood that when the coupling heatsup while operating, the centering rings and 11 tend to move away fromthe convex cylindrical faces 14 of the pole piece halves. The peripheralgap 16 (FIGS) is thus reduced, but at no time is the free expansion ofthe rings 10 or 11 hindered by the pole piece halves 3 and 4. When hot,the rigorous centering of the pole piece halves 3 and 4 on the cheeks 5and 6 is no longer ensured by the rings 10 and 11. It is producedautomatically under the action of the powder contained in the air gap 2,this powder thus being made compact by the action of the magnetic field.

When cooling, the centering is again guaranteed by the inner faces suchas 12 of the rings 10 and 11 which reassume contact with the convexcylindrical faces such as 14 or the pole piece halves 3 and 4.

There is provided between the pole piece halves 3 and 4, a free space 19(FIG. 4) which extends until it opens into the air gap 2. Each polepiece half opens into the air gap by a bevel 20 or 21.

Above this bevel there is cut a second annular groove, indicated by thereference numeral 22 for the pole piece half 3 and by the reference 23for the pole piece half 4 (FlG.4). These two grooves 22 and 23 arecoaxial and open out opposite each other. The edges of a cylindricalsleeve 24 made of an amagnetic material such as stainless steel, bronze,brass or a light alloy are engaged in these grooves. It can slide inaxial direction (double arrow 25) and its air-tightness is ensured bytwo annular seals 26 and 27 located at the base of the grooves 22 and23.

These seals are made of a deformable material able to resist heat, i.e.,a synthetic resin polymer such as a product known under the trade nameTEFLON.

in its center, the sliding sleeve 24 comprises an annular boss 28 whichprojects radially inwardly toward the air space 2 and the inner face 29of which has the same diameter as the inner wall 30 or 31 of the polepiece halves 3 and 4.

[t is understood that, even if the components of the coupling aresubjected to a sudden heating which causes a high gradient oftemperature in the vicinity of the air gap 2, the metal of the polepiece halves 3 and 4 can expand freely on either side of the sleeve 24without risking causing any thermal stresses. On the other hand, thepresence of the sleeve 24 prevents the pow der from leaving the air gap2 to enter the free space 19.

The free sliding of the sleeve 24 is facilitated by preventing powderfrom packing between its annular boss 28 and the pole piece halves 3 and4. For this, the inlets 20 and 21 of the pole piece halves 3 and 4 arebevelled, and the boss 29 is also provided with bevelled lateral faces32 and 33.

Due to the presence of this boss 28, the thickness of the layer ofpowder under the sleeve 24 is not greater than in the rest of the airgap 2. Thus, the magnetic leakage through the shunt formed by the layerof pow der is not increased.

What is claimed is:

1. An electromagnetic powder coupling, comprising:

an inner rotor;

an outer rotor formed by two pole pieces disposed around and spacedapart from said inner rotor;

an air space defined by said inner rotor and said outer rotor adopted tocontain a powdered metal therein;

means defining a first annular groove formed in an end of each of saidpole pieces comprising a convex cylindrical face and an innercylindrical face;

two lateral cheek pieces disposed at opposite ends of said outer rotoradopted to center said pole pieces comprising said outer rotor with saidinner rotor to produce a uniform symmetric air space therebetween eachof said cheek pieces having a centering ring disposed thereon defining aconcave cylindrical face and an outer cylindrical face, said concavecylindrical face being adopted to mate contiguously when cold againstsaid convex cylindrical face of said annular groove in said pole pieces;

a radial clearance defined by said outer cylindrical face of saidcentering ring of each of said cheek pieces and said inner cylindricalface of each of said annular grooves in said pole pieces when they arecold to allow for thermal expansion of said centering rings and saidcheek pieces as they become hot;

an excitation coil located partially in each of said pole pieces at aninterface between said pole pieces, the face of each of said pole piecescomprising said interface being opposite said ends thereof which containsaid first annular grooves;

means defining a free space in each of said pole pieces at saidinterface between said pole pieces, said free spaces being disposedcoaxially with each other and extending radially from said excitationcoil to said air space;

means defining a second annular groove in each of said pole pieces atsaid interface between said pole pieces, said second annular groovesbeing disposed coaxially with each other and radially located betweensaid excitation coil and said air space;

an amagnetic sleeve partially disposed in each of said annular groovesin said pole pieces coaxially therewith and adopted to beaxially-slidable therein to allow said pole pieces to expand freelyindependently of each other, and to prevent powdered metal from passingfrom said air space to said excitation coil; and

an annular seal located in each of said second annular grooves, eachdisposed between the base of a different one of said grooves and saidamagnetic sleeve to provide an air tight fit between each of saidgrooves and said sleeve.

2. A coupling as defined in claim 1, further characterized in that:

said coaxial sleeve has a radially inwardly projecting annular bosshaving inclined lateral faces; and

a portion of each of said pole pieces located between said coaxialsleeve and said air space having bevelled lips adjacent said inclinedfaces of said boss of said sleeve sloping in a generally oppositedirecsaid inclined faces of said boss and said opposite bevelled facesof said pole pieces adjacent said boss prevent powdered metal frompacking between said sleeve and said annular boss. 3. A coupling asdefined in claim 2, further characterized in that said radially inwardlyprojecting annular boss has an inner face of the same diameter as aninner wall of said pole pieces such that a portion of said air spacelocated between said innerrotor and said boss is substantially the sameas the thickness of the portion of said air gap between said inner rotorand said outer rotor,

thus preventing an increase in the magnetic leakage through the magneticshunt formed by the layer of metal powder contained in said air space.4. A coupling as defined in claim 1 further characterized in that saidannular seals are fabricated of a deformable material able to resistheat.

5. A coupling as defined in claim 4 further characterized in that saidseal is fabricated of a synthetic resin polymer.

6. A coupling as defined in claim 5 further characterized in that saidsynthetic resin polymer is TEFLON.

7. A coupling as defined in claim 1 further characterized in that saidcheek pieces are fabricated of a material having a greater coefficientof expansion than that of said pole pieces.

8. A coupling as defined in claim 7 further characterized in that:

said cheek pieces are fabricated of an amagnetic material; and

said pole pieces are fabricated of soft steel.

9. A coupling as defined in claim 1, further characterized in that saidcoupling is fastened together by a plurality of fasteners which passentirely through both of said cheek pieces and both of said pole pieces.

1. An electromagnetic powder coupling, comprising: an inner rotor; an outer rotor formed by two pole pieces disposed around and spaced apart from said inner rotor; an air space defined by said inner rotor and said outer rotor adopted to conTain a powdered metal therein; means defining a first annular groove formed in an end of each of said pole pieces comprising a convex cylindrical face and an inner cylindrical face; two lateral cheek pieces disposed at opposite ends of said outer rotor adopted to center said pole pieces comprising said outer rotor with said inner rotor to produce a uniform symmetric air space therebetween each of said cheek pieces having a centering ring disposed thereon defining a concave cylindrical face and an outer cylindrical face, said concave cylindrical face being adopted to mate contiguously when cold against said convex cylindrical face of said annular groove in said pole pieces; a radial clearance defined by said outer cylindrical face of said centering ring of each of said cheek pieces and said inner cylindrical face of each of said annular grooves in said pole pieces when they are cold to allow for thermal expansion of said centering rings and said cheek pieces as they become hot; an excitation coil located partially in each of said pole pieces at an interface between said pole pieces, the face of each of said pole pieces comprising said interface being opposite said ends thereof which contain said first annular grooves; means defining a free space in each of said pole pieces at said interface between said pole pieces, said free spaces being disposed coaxially with each other and extending radially from said excitation coil to said air space; means defining a second annular groove in each of said pole pieces at said interface between said pole pieces, said second annular grooves being disposed coaxially with each other and radially located between said excitation coil and said air space; an amagnetic sleeve partially disposed in each of said annular grooves in said pole pieces coaxially therewith and adopted to be axially-slidable therein to allow said pole pieces to expand freely independently of each other, and to prevent powdered metal from passing from said air space to said excitation coil; and an annular seal located in each of said second annular grooves, each disposed between the base of a different one of said grooves and said amagnetic sleeve to provide an air tight fit between each of said grooves and said sleeve.
 2. A coupling as defined in claim 1, further characterized in that: said coaxial sleeve has a radially inwardly projecting annular boss having inclined lateral faces; and a portion of each of said pole pieces located between said coaxial sleeve and said air space having bevelled lips adjacent said inclined faces of said boss of said sleeve sloping in a generally opposite direction to that of said inclined lateral faces of said sleeve, said inclined faces of said boss and said opposite bevelled faces of said pole pieces adjacent said boss prevent powdered metal from packing between said sleeve and said annular boss.
 3. A coupling as defined in claim 2, further characterized in that said radially inwardly projecting annular boss has an inner face of the same diameter as an inner wall of said pole pieces such that a portion of said air space located between said inner rotor and said boss is substantially the same as the thickness of the portion of said air gap between said inner rotor and said outer rotor, thus preventing an increase in the magnetic leakage through the magnetic shunt formed by the layer of metal powder contained in said air space.
 4. A coupling as defined in claim 1 further characterized in that said annular seals are fabricated of a deformable material able to resist heat.
 5. A coupling as defined in claim 4 further characterized in that said seal is fabricated of a synthetic resin polymer.
 6. A coupling as defined in claim 5 further characterized in that said synthetic resin polymer is TEFLON.
 7. A coupling as defined in claim 1 further characterized in that said cheek pieces are fabricated of a material having a greater coefficient of expansion than that of said pole piecEs.
 8. A coupling as defined in claim 7 further characterized in that: said cheek pieces are fabricated of an amagnetic material; and said pole pieces are fabricated of soft steel.
 9. A coupling as defined in claim 1, further characterized in that said coupling is fastened together by a plurality of fasteners which pass entirely through both of said cheek pieces and both of said pole pieces. 